This invention relates generally to deflection yokes, and in particular to deflection yokes for use with monochrome or color television receivers wherein vertical deflection windings are toroidally wound on a ferrite core.
In conventional monochrome and color television receivers, a cathode-ray tube (CRT) is provided with a deflection yoke assembly for deflecting electron beams generated within the CRT to produce a display raster. In the case of color television receivers, the deflection yoke performs the additional function of converging the beams provided by three separate electron guns. Typically, deflection yoke assemblies include a frusto-conical ferrite core dimensioned to surround the relatively narrow neck portion of the CRT where it joins the flared portion of the tube envelope. Frequently, the deflection yoke includes a pair of diametrically opposed toroidally wound windings on the ferrite core for causing vertical deflection of electron beams, while a pair of saddle-shaped windings, disposed between the interior surface of the core and the external surface of the envelope, provide horizontal deflection of the beam. As the quality of the display is greatly affected by the configuration and location of the deflection windings, much effort has been expended in developing winding distributions which provide displays of superior quality.
Since the path distances travelled by individual electrons of the electron beam vary according to the location on the screen to which the beam is directed, use of uniform magnetic deflection fields would result in a distorted raster. Accordingly, non-uniform fields are used to obtain a non-distorted raster. Such non-uniform fields are produced by altering the shape of the deflection windings as well as the distribution of turns within individual windings. Cosine windings, wherein the turns density varies according to the cosine of an angle, constitute one form of distribution frequently used. Other winding distributions, which may involve cross-overs of individual windings, may also be used.
Once an acceptable winding distribution has been identified, it is necessary for a deflection yoke manufacturer to develop a method for accurately and economically reproducing the desired distribution over a large quantity of cores. One technique developed for this purpose is to attach plastic rings having notches, ridges, or pins to either or both edges of the ferrite core. The windings overlap the rings, which serve to maintain the position of the windings relative to the core. The technique is attractive, particularly where the winding distribution is complex since it is relatively easy to accurately mold a great number of precisely dimensioned notches in the plastic rings. However, the additional manufacturing steps required raise manufacturing costs.
The present invention overcomes the disadvantages of prior techniques by directly providing at selected locations in the ferrite core a number of notches of preselected depth and width. In winding the deflection windings of the yoke, wire is placed on the core so that each notch is filled before winding commences on the next adjacent notch. Thus, each turn is substantially parallel with the others and wire cross-overs are eliminated. The technique of forming the notches directly in the core avoids the economic disadvantage associated with installing plastic rings, and the relatively large dimension of each notch avoids the difficulty associated with accurately forming a large number of small, precisely dimensioned notches directly in the core, since dimensional changes resulting from shrinkage of the core during firing after casting are less significant with the relatively larger notches.
The present invention has the further advantage that less time is required to form the windings since the position of each turn within a notch is not as critical as with notches of lesser width. Furthermore, the accurate positioning of the windings by reason of their being disposed in accurately positioned notches improves linearity in the completed yoke, while lower inter-winding capacitance, resulting from the elimination of wire cross-overs, reduces distortion in the display such as that caused by "ringing". Additionally, providing notches directly in the ferrite core allows the linear dimension of the core to be increased without requiring a corresponding increase in the length of the vertical windings placed thereon. The effect of this is that sensitivity of the horizontal windings may be increased by extending the core along those portions between the vertical windings without simultaneously increasing the physical dimensions, and hence the cost, of the vertical windings.
Accordingly, it is a general object of the present invention to provide a new and improved deflection yoke for use with cathode-ray tubes.
It is a further object of the present invention to provide a deflection yoke which is more economical to manufacture and more accurate and repeatabe in performance.